Nine people were killed in a massacre in Medellin, heralding a new round of violence as different criminal factions seek to establish hegemony of the underworld in Colombia‘s second-largest city.

On the night of December 30, 16 people arrived at a mansion in Envigado, on the outskirts of Medellin. The next morning the cleaning lady arrived to find the bodies of nine of them spread across two floors. The neighbors did not hear the sound of shots, leading police to believe that the killers used silencers.

Medellin’s police chief, General Yesid Vasquez, said that intelligence suggested that the mansion was the site of a meeting between senior members of the city’s mafia, planning to celebrate and to discuss who would be promoted within the structure, to replace five leaders arrested during 2012.

Among the dead were three identified members of the Medellin mafia, known as the “Oficina de Envigado.” They were Jorge Mario Marin, alias “El Morro;” Hugo Fernando Uran Mesa, alias “El Panadero,” and Carlos Andres Gonzalez Hernandez, alias “El Mosco.”

There were four young women among the dead, all found in a single room, three of them with their hands still pressed against their faces. Police believe they had been invited to provide entertainment for the mafia bosses. Police seized pistols, a submachine gun, and an AK-47 at the house. It seems their owners had not had a chance to reach their weapons before being killed.

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Since the extradition in 2008 of Diego Murillo, alias “Don Berna,” the then undisputed head of the Oficina de Envigado, there has been a bitter war between rival factions to take over control of the city and reunite the Oficina. The last man to seek his throne was Erick Vargas Cardenas, alias “Sebastian,” captured by police in August last year.

Medellin has always had several hundred different street gangs, or “combos.” Many of these gangs provided the muscle that Pablo Escobar needed for his Medellin Cartel.  After the death of Escobar on a Medellin rooftop in December 1993, Don Berna took over the city, resisting any challenges to his power. Over the years several of the gangs became super combos, powerful organized crime syndicates in their own right, dominating different neighborhoods of the city.

Among those killed in the massacre were senior members of two of the city’s super combos.  “El Morro” was believed to be the head of powerful gang “Trianon,” while “El Panadero” and  “El Mosco” were from La Terraza, a group that specializes in assassination, providing services throughout Colombia and even abroad. These men were all ambitious middle ranking members of the Medellin mafia, all looking to move up.

The key question is who were the other men who arrived at the celebrations and later left. Police believe these men to be the killers and that they are other senior members of the Oficina. There was no evidence of a shootout, or forced entry, leading the police to believe that the killers were also invited guests. There are three aliases that different sources have provided as among the guests: “Fredy Colas,” “Pichi” and “Barny.” Freddy Colas is the alias of Fredy Alexander Duarte Diaz, who was the right hand of Sebastian, the man who almost managed to take control of the Oficina before his arrest last year. The other two are believed to be the bosses of combos in the Candelaria and Aranjuez sectors of Medellin.

However it is not only the Oficina that is eyeing the criminal prize of Medellin. From their stronghold to the north, the Urabeños are looking to take over the city’s underworld, allowing them to unite the city with the Caribbean coast where they control drug trafficking routes. Now perhaps the most powerful criminal syndicate in the country, the Urabeños have already forged alliances with combos in various parts of Medellin, and are slowly expanding their influence in the city.

General Vasquez believes that the massacre heralds a new chapter of infighting between different factions of the Oficina, and that 2013 will be yet another violent year for the city.

Jeremy McDermott is co-founder and co-director of InSight Crime. McDermott has more than two decades of experience reporting from around Latin America. He is a former British Army officer, who saw active...